178 Count de Bournon's Description of 
pyramid. (Fig. 5.) The crystal is still more frequently found 
in the form of a long tetraedral rhomboidal prism, of 84,° and 
9 6°, terminated by a diedral apex, with isosceles triangular 
planes, which are placed on the angles of 84°, and meet in an 
angle of 112 0 . (Fig. 6.) 
Most commonly, both in the perfect and the lengthened 
octaedron, the angles of 96° are replaced by a plane, which is 
equally inclined on the adjacent sides, (Fig. 7.) and is fre- 
quently very broad : (Fig. 8.) then the tetraedral prism of 84° 
and 96°, is changed into a flat hexaedral prism, having two 
angles of 84°, and the other four of 138°. I never saw the 
angles of 84° replaced. 
The average specific gravity of this arseniate of copper, taken 
on five pure pieces, was 4,280. 
It is sufficiently hard to scratch fluor spar ; but is not hard 
enough to scratch glass. 
Its usual colour is a brown, or bottle green, so dark that the 
crystals appear of a blackish colour, when they are not opposed 
to the light ; sometimes, but very seldom, in the regular crys- 
tals which happen to be rather thicker, this colour is a clearer 
green ; in other specimens, the crystals have a yellowish cast, 
and the surface then often reflects the light of a golden 
tint. 
The transparency of this species is generally pretty great. 
It is not always crystallized in a determinate form, but is an 
absolute Proteus, both with respect to the different forms in 
which it appears, and the various colours it exhibits. I have 
observed the five following varieties of it. 
